Guide Lowpres

8/9/2019 Guide Lowpres

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DESIGN AND SPECIFICATION GUIDELINES

FOR LOW PRESSURE SEWER SYSTEMS

PREPARED BY

A TECHNICAL ADVISORY COMMITTEE FOR

THE STATE OF FLORIDA DEPARTMENT

OF ENVIRONMENTAL REGULATION

June1981


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DESIGN AND SPECIFICATION GUIDELINES

FOR LOW PRESSURE SEWER SYSTEMS

Prepared by a

Technical Advisory Committee

Dan Glasgow, Editor and Chairman

William C. Bowne

Thomas H. Braun

Edward T. Knudsen

James F. Kreissl*

Paul A. Kuhn*

Robert E. Langford

Patricia H. Lodge

David A. Maurer

James E. Santarone

Harold E. Schmidt

B. Jay Schrock

Dr. G. J. Thabaraj

Richard D. Vaughan*

John G. Hendrickson

Staff assistance was provided by the General Development Corporation,Miami, Florida

* Principal Contributing Authors


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FOREWORD

In April 1980, Mr. Jake Varn, Secretary of the State of Florida Department of Environmental

Regulation authorized the formation of a Technical Advisory Committee to prepare

Departmental Design and Specifications Guidelines for Low Pressure Sewer Systems. This

document was prepared with the sponsorship of the General Development Corporation with

review and staff assistance provided by Dr. G. J. Thabaraj and Mr. James E. Santarone of the

State of Florida Department of Environmental Regulation. The contents of this document are

supplemental to and made a part of the Rules of the State of Florida Department of

Environmental Regulation, Chapter 17-6, Florida Administrative Code.

Throughout this document, references are made to recognized product and installation

standards. Where a conflict may exist between the cited standard and this document, therequirements set forth in this document shall prevail unless otherwise authorized in writing from

the Department of Environmental Regulation.


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TABLE OF CONTENTS

Titlepage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

Chapter I DESIGN. . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1

A. General Considerations. . . . . . . . . . . . . . . . . . . . . . . I-1

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . I-1

2. Facility Planning Information. . . . . . . . . . . . . . . . . . I-1

3. System Layout and Alignment. . . . . . . . . . . . . . . . . . I-7

a. Pressure sewer main. . . . . . . . . . . . . . . . . . . . I-7

b. On-lot facilities. . . . . . . . . . . . . . . . . . . . . . I-10

4.

Design Flows. . . . . . . . . . . . . . . . . . . . . . . . . I-14

5. Hydraulics. . . . . . . . . . . . . . . . . . . . . . . . . . I-16

6. Contingency Planning . . . . . . . . . . . . . . . . . . . . . I-20

7. Mainline Appurtenances. . . . . . . . . . . . . . . . . . . . I-21

8.

Treatment and Characteristics of Low Pressure

Sewer System Wastewaters. . . . . . . . . . . . . . . . . . I-22

9.

Management Implications. . . . . . . . . . . . . . . . . . . . I-24

B.

Basic Design. . . . . . . . . . . . . . . . . . . . . . . . . . . I-26

1. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . I-26

2. Design Sequence. . . . . . . . . . . . . . . . . . . . . . . . I-26

Chapter II ON-LOT FACILITIES CONSTRUCTTON. . . . . . . . . . . . II-1

A.

Septic Tank and Wetwell. . . . . . . . . . . . . . . . . . . . . . II-1

1. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . II-1

2.

Sizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-1

3. Septic Tank Structural Design. . . . . . . . . . . . . . . . . . II-1

4.

Corrosion of Materials Used in Septic

Tank and Wetwell Construction. . . . . . . . . . . . . . . . II-4

5. Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . II-4

6.

Installation of Septic Tanks. . . . . . . . . . . . . . . . . . . II-4


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B. Septic Tank Construction . . . . . . . . . . . . . . . . . . . . . II-5

1. Concrete Septic Tanks . . . . . . . . . . . . . . . . . . . . . II-5

2. Plastic Septic Tanks . . . . . . . . . . . . . . . . . . . . . . II-5

3.

Metal Septic Tanks. . . . . . . . . . . . . . . . . . . . . . . II-5

4.

Existing Septic Tanks. . . . . . . . . . . . . . . . . . . . . . II-6

5. Inlets and Outlets . . . . . . . . . . . . . . . . . . . . . . . II-6

6. Septic Tank Risers and Wetwell Covers . . . . . . . . . . . . . II-6

C.

Appurtenances. . . . . . . . . . . . . . . . . . . . . . . . . . . II-6

1. Grinder Pumps . . . . . . . . . . . . . . . . . . . . . . . . II-6

2. Effluent Pumps. . . . . . . . . . . . . . . . . . . . . . . . II-9

3. Wetwell Appurtenances. . . . . . . . . . . . . . . . . . . . . II-10

a.

Internal discharge piping. . . . . . . . . . . . . . . . . . II-10

b.

Check valves. . . . . . . . . . . . . . . . . . . . . . . . II-10

c. Hose connections. . . . . . . . . . . . . . . . . . . . . . II-10

d. Gate or ball valves. . . . . . . . . . . . . . . . . . . . . II-10

e. Quick disconnect couplings. . . . . . . . . . . . . . . . . II-10

f. Level sensors. . . . . . . . . . . . . . . . . . . . . . . II-11

g. Sealing of adaptors passing through chamber. . . . . . . . . II-12

D. Electrical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-12

1. Grinder Pump Control Systems. . . . . . . . . . . . . . . . . II-12

2. Septic Tank Effluent Pump Control Systems. . . . . . . . . . . II-13

3. Pump and Alarm Systems. . . . . . . . . . . . . . . . . . . . II-13

E.

Existing Septic Tank Overflows and Drainfield Lines. . . . . . . . . II-13

1. Grinder Pumps. . . . . . . . . . . . . . . . . . . . . . . . . II-13

a. Holding Tank. . . . . . . . . . . . . . . . . . . . . . . II-13

b. Existing on-site septic tank. . . . . . . . . . . . . . . . . II-14

2.

STEP Systems. . . . . . . . . . . . . . . . . . . . . . . . . II-14

a. Existing drainfield. . . . . . . . . . . . . . . . . . . . . II-14

b. Newdrainfield. . . . . . . . . . . . . . . . . . . . . . . II-14

3. Venting. . . . . . . . . . . . . . . . . . . . . . . . . . . . II-14

F.

Building Sewer. . . . . . . . . . . . . . . . . . . . . . . . . . II-15


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G. ServiceLines . . . . . . . . . . . . . . . . . . . . . . . . . . . II-15

1. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . II-15

2. Service Line Materials. . . . . . . . . . . . . . . . . . . . . II-15

3.

Check Valves. . . . . . . . . . . . . . . . . . . . . . . . . II-15

4.

On/Off Valves and Corporation Stops. . . . . . . . . . . . . . II-16

5. Service Line Installations. . . . . . . . . . . . . . . . . . . . II-16

6. Separation of Waterlines and Street Crossings. . . . . . . . . . II-16

H.

Connection to Pressure Sewer Main. . . . . . . . . . . . . . . . . II-17

1. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . II-17

2. Connection Methods. . . . . . . . . . . . . . . . . . . . . . II-17

3. Wye and tee connections. . . . . . . . . . . . . . . . . . . . II-17

4.

Wet tap connections. . . . . . . . . . . . . . . . . . . . . . II-17

5.

Polyethylene service lines. . . . . . . . . . . . . . . . . . . . II-17

6. Valves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-17

I. Pipe Installation Service. . . . . . . . . . . . . . . . . . . . . . II-18

Chapter III PRESSURE SEWER MAIN CONSTRUCTION . . . . . . . . . III-I

A. Pressure Sewer Main Pipe Materials . . . . . . . . . . . . . . . . III-1

1. Thermoplastic Sewer Main Pipe Materials. . . . . . . . . . . . III-1

a. General. . . . . . . . . . . . . . . . . . . . . . . . . . III-1

b. Polyvinyl chloride (PVC) pressure pipe. . . . . . . . . . . III-1

c. Polyethylene (PE) pressure pipe. . . . . . . . . . . . . . . III-2

d.

Acrylonitrile butadiene-styrene (ABS) pressure pipe. . . . . III-2

e. Thermoplastic pressure pipe fittings. . . . . . . . . . . . . III-2

f. Pressure sewer pipe identification. . . . . . . . . . . . . . III-3

g. Specifications. . . . . . . . . . . . . . . . . . . . . . . III-3

2.

Fiberglass Reinforced Thermosetting

Resin (FTR) Pressure Pipe. . . . . . . . . . . . . . . . . III-3

3.

Ductile Iron (DI) Pressure Pipe. . . . . . . . . . . . . . . . . III-4


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B. Pressure Sewer Pipe Installation. . . . . . . . . . . . . . . . . . . III-4

1. Location and Depth of Cover. . . . . . . . . . . . . . . . . . III-4

2. Excavation and Backfill. . . . . . . . . . . . . . . . . . . . III-5

a.

General. . . . . . . . . . . . . . . . . . . . . . . . . . III-5

b.

Trench excavation. . . . . . . . . . . . . . . . . . . . . III-5

c. Rock excavation. . . . . . . . . . . . . . . . . . . . . . III-5

d. Excavation backfill. . . . . . . . . . . . . . . . . . . . . III-5

3.

Pressure Sewer Main Pipe Laying and Jointing. . . . . . . . . . III-6

a. General. . . . . . . . . . . . . . . . . . . . . . . . . . III-6

b. Jointing. . . . . . . . . . . . . . . . . . . . . . . . . . III-7

c. Plugs, anchorage and thrust restraint. . . . . . . . . . . . . III-7

4.

Flushing, Leakage, Testing and Repair. . . . . . . . . . . . . . III-8

a.

Flushing. . . . . . . . . . . . . . . . . . . . . . . . . . III-8

b. Pressure test. . . . . . . . . . . . . . . . . . . . . . . . III-8

c. Leakage test. . . . . . . . . . . . . . . . . . . . . . . . III-8

5. Special Construction Provisions. . . . . . . . . . . . . . . . . III-9

a. Roadway crossings. . . . . . . . . . . . . . . . . . . . . III-9

b. Railroad crossings. . . . . . . . . . . . . . . . . . . . . III-9

c. Bridge crossings. . . . . . . . . . . . . . . . . . . . . . III-10

d. Potable water supply crossing. . . . . . . . . . . . . . . . III-10

e. Installation in vicinity of potable water supply well. . . . . . III-11

6. Appurtenances. . . . . . . . . . . . . . . . . . . . . . . . . III-11

a.

Air release facilities. . . . . . . . . . . . . . . . . . . . III-11

b. Connections and tapping. . . . . . . . . . . . . . . . . . III-11

c. Appurtenance boxes and vaults. . . . . . . . . . . . . . . III-12

d. Valves and valve boxes. . . . . . . . . . . . . . . . . . . III-12

e.

Cleanouts. . . . . . . . . . . . . . . . . . . . . . . . . III-13

f. Terminal manhole connections. . . . . . . . . . . . . . . III-13

g. Pipe locating marking tape. . . . . . . . . . . . . . . . . III-13

7. Record Drawings . . . . . . . . . . . . . . . . . . . . . . . III-14

8.

Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . III-14

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x


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LIST OF TABLES

Table I-I Growth and Development Factors. . . . . . . . . . . . . . . . . I-2

Table I-2 Natural and Physical Features. . . . . . . . . . . . . . . . . . . I-4

Table I-3 Typical Sources of Information on On-Site Systems. . . . . . . . . I-5Table I-4 Preliminary Regulatory Constraints. . . . . . . . . . . . . . . . I-6

Table I-5 PVC Pipe Characteristics. . . . . . . . . . . . . . . . . . . . . I-17


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LIST OF FIGURES

Figure I-1 Typical Pressure Sewer Layout. . . . . . . . . . . . . . . . . . I-8

Figure I-2 Pressure Sewer Schematics. . . . . . . . . . . . . . . . . . . . I-9

Figure I-3 Recommended Design Flow. . . . . . . . . . . . . . . . . . . I-15

Figure I-4 Pipe Sizing Procedure. . . . . . . . . . . . . . . . . . . . . . I-19

Figure II-1 Typical Pressurization Unit (PU) Installation. . . . . . . . . . . II-2

Figure II-2 Typical Septic Tank Effluent Pump Systems. . . . . . . . . . . II-3

Figure II-3 Typical Grinder Pump (GP) Systems. . . . . . . . . . . . . . . II-7

Figure II-4 Typical Head-flow Characteristics for Centrifugal

And Semi-positive Displacement Pumps. . . . . . . . . . . . . II-8

Figure III-1 Recommended Valve and Cleanout Arrangements

With Provision for Hose Connections. . . . . . . . . . . . . . III-15

Figure III-2 Recommended Valve Box and Cleanout Arrangements

Along Straight Runs and at Changes in Direction. . . . . . . . . III-16

Figure III-3 Suggested Valve Box Cleanout Arrangements at Junction

Of Pressure Sewer Mains. . . . . . . . . . . . . . . . . . . . III-17

Figure III-4 Recommended Valve Box and Cleanout Arrangements at

End of Pressure SewerMain. . . . . . . . . . . . . . . . . . III-18

Figure III-5 Terminal Manhole Connection. . . . . . . . . . . . . . . . . III-19

Figure III-6 Methods of Providing Service Connections to Pressure

Sewer Mains. . . . . . . . . . . . . . . . . . . . . . . . . . III-20


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CHAPTER I

DESIGN

Section A. GENERAL CONSIDERATIONS

Part 1. Introduction

In order to properly choose and design any wastewater collection facility it is necessary to

define the service area in geographical, topographical, geological, climatological, sociological,

and economic terms. The complexity of required definition may vary with circumstances from a

relative minimum with a planned development to a maximum for an existing community.

Likewise, the difficulty of the design process varies in the same manner. The planned

community usually can be characterized as a situation where optimum solutions are possible, the

lines of communication simple and direct, and constraints and their sources fewer and more

technologically based. Existing communities generally present situations and solutions which

are often based on less technical aspects and increased public relations. The considerations of

this document are based primarily on the technological problems of pressure sewer systems.

Part 2. Facility Planning Information

The initial step in any planning effort is to define the service area. Information which is

potentially useful for facilities planning includes:

a. service area growth and development;

b.

natural and physical features;

c. existing wastewater and residuals disposal practices; and

d. regulations and institutions.

For an existing community Table I-1 offers an example of growth and development factors

and potential information sources. For a planned community, the design should be based on the

projected population growth and those socioeconomic factors which would provide some basis

for determining reasonable user charges for the wastewater collection and treatment system


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I-2

TABLE I-1

GROWTH AND DEVELOPMENT FACTORS

U.S.Census

StatePlanningAgen

cy

StateOfficeof

EmploymentSecurit

y

RegionalPlanning

Agency/208Agency

LocalPlanning

Agency

Local

Administrator

Local

TaxAssessor

Businessand

Institutional

Survey

LocalChamber

OfCommerce

Existing Population 0 0 *

Historical Population * *

Population Characteristics for Last

Two Federal Census Periods-Age, Cohorts,

Median Family Income

*

Population Projections - Local and Regional

During Service Design Period* * *

Existing Employment For Individual

Business and Institutions

0 * *

Economic Base/Employment Projections * 0 0

Existing Property Assessment Valuation *

Property Tax Rate *

Equalized Tax Rate *

Annual Revenues by Major Source *

Annual Expenditures by Major ServiceCategories

*

* Indicates Preferred Data Source0 Indicates Alternative Data Sources

Factor

Source


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during the planning period. Anticipated growth patterns can affect pressure sewer designs in

several ways.

Table I-2 presents a list of typical natural and physical features and potential informationsources. These features can affect the design and construction of pressure sewers.

For existing communities relatively complete information on existing wastewater and

residuals disposal systems must be obtained. Where sewers and central treatment facilities exist,

the existing data sources are relatively easy to locate. Where on-site disposal has been

widespread the data are generally more diffuse. Table 1-3 lists typical sources of information on

on-site systems. In previously sewered communities a new pressure sewer design will be

affected by the present condition and capacity of the existing system. For example, an existing

sewer with excess capacity may be the logical receptor of the pressure sewer wastewater

discharge, while an existing sewer without available capacity would suggest study of alternative

approaches such as infiltration/inflow reduction, water conservation programs to create the

necessary capacity or separate treatment and disposal sites for the pressure sewer. Where

existing on-site systems have a varied performance, e.g., isolated problem areas, pressure sewer

designs should consider the historical performance in determining pressure sewer main location,

phasing, construction, and terminal treatment system location and design.

Local regulations and institutions represent major determinants of pressure sewer designs.Table 1-4 indicates the preliminary regulatory constraints which should be determined prior to

design. Institutional arrangements in the service locality must be determined to ascertain

available mechanisms for pressure sewer management programs. Existing institutional entities

may be easily adaptable to managing these systems in some locations, while establishment of

new institutions may be required in others.


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TABLE I-2

NATURAL AND PHYSICAL FEATURES

NATIONAL

WEATHER

SERVICE

LOCALAIR

PORTS

LOCALUNIVERSITY

U.S.G.S.

HUD

SOILCONSERVATION

SERVICE

208AGENC

Y

STATEOFF

LA.DEPT.

OFENVIRO

NMENTAL

REGULATION

LOCALTAX

ASSESSOR

LOCALWA

TER

MANAGEM

ENT

DISTRICT

LOCALHEA

LTHDEPT.

Annual Precipitation 0 0

Mean Temperature 0 0

Temperature Ranges 0 0

Humidity 0 0

Prevailing Winds 0 0CLIMATE

Evaporation Potential

Topography

Kit Limitation Maps

Interpretive Reports

SOILS

Frost Depth 0

Wetlands

Flood Hazard Areas 0

Drainage Areas

Flow Characteristics

Water Quality Data

Existing Water Quality Classification

SURFACEWATER--

STREAMS/RIVERS

Existing Uses of Water 0

Drainage Area

Stream Sources

Elevation

Acreage

Mean Depth 0 0

Ownership

Water Quality Data 0 0

Existing Water Quality Classification SURFACEWATER--

PONDS/LAKES

Existing Uses of Water 0

Areal Extent of Aquifers 0 0

Seasonal Groundwater Levels 0

Saturated Thickness of Aquifers 0 0

Transmissivity

Existing Public Wells

Average Daily Drawdown for Wells GROUNDWATER

Water Quality Data 0 0 0 0

Indicated Preferred Data Source

0 Indicates Alternative Data Sources

Data Source

Data Element


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Part 3. System Layout and Alignment

One of the first tasks in the design of a pressure sewer is the preparation of a schematic of

the system. The principal purpose is to minimize the length of the lines in the system just as withconventional gravity sewers. However, the relatively unconstrained alignment requirement and

lower construction cost per lineal foot of the pressure sewer provides an opportunity to exercise

imagination and demonstrate good judgement.

a) Pressure sewer main

Several factors to be considered in developing a preliminary layout of a pressure sewer main

include:

1) right of way, access and easements

2) resident and traffic disruption

3) dendriform vs. grid horizontal layout

4) potential main breakage, repair time, and users affected

5) pressure sustaining

6) air entrainment

Presently both dendriform and grid horizontal layouts are used. Dendriform layouts

theoretically require the least amount of pressure sewer main construction. However, where each

unit feeds the main sewer, any damage to the main sewer would interrupt service to all upstream

connections. The grid layouts, as employed in water supply systems, overcome the loss of

service problems, but would result in the uneven flow patterns which are a particularly difficult

problem in systems where scouring velocities are integral to their proper functioning.

A popular compromise to either the dendriform or grid layout has been the clustered feeder

approach as depicted in Figure I-1, wherein smaller branched systems service multiple

connections and feed into the main sewer. This main sewer may be either a pressure or gravity

sewer with the clustered feeder layout, where service or mainline breakage is more likely only


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FIGURE I-1. Typical pressure sewer layout


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FIGURE I-2. Pressure Sewer Schematics


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to affect the particular cluster in which breakage occurs and flows would remain more

predictable as in the dendriform layout. Additionally, a reduction of service interruption could

be accomplished by the installation of a connector line between clusters as shown in Figure I-2.

The connector line would normally be valved from service and could be opened to serviceotherwise isolated dwellings.

Vertical alignment considerations will also impact the horizontal layout. Ideally, a pressure

sewer would be optimal if it were provided a nearly constant upward grade from its farthest point

to its terminus and thereby eliminate the need for air release valves, pressure sustaining valves or

similar appurtenances. These concerns should be considered during the design stage although

the final pipe location will often be determined in the field at the -time of construction.

The pressure sewer systems shall be able to handle the wastewater generated by the design

population of the service area. In the example where there are several underdeveloped lots

within the service area, the designer must consider if system capacity will be sufficient to handle

the design discharge. The designer shall analyze the capacity of the system to determine the

Units of development beyond the design population which the system can handle through special

approaches.

b) On-lot facilities

The major capital and operation and maintenance (O/M) costs of pressure sewers have

historically related to the on-lot or pressurization facilities. Several considerations must be

factored into on-lot pressure sewer system design, and include:

1) type of pressurization system

2) single vs. multiple service

3) location of pressurization system

4) alarms and controls

5) aesthetics and safety problems

6) serviceability of components


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7) materials of construction

8) electrical problems

9) contingency problems

The first on-lot facility design decision is the specification of the generic type of

pressurization unit (PU). This will have specific effects on the remainder of the system design.

However, unless local circumstances preclude one of the two primary alternatives, both the

grinder pump (GP) and septic tank effluent pump (STEP) system should be considered. A

comparison table of the two alternatives is shown below:

Item of Comparison GP STEP

*Capital cost: on-lot

pressurization unit more lessappurtenances less more

*Capital cost: main similar similar

*O/M cost on-lot

pressurization unit more less

residuals handling less more

*O/M cost: main

present population similar similar

design population

present population more lessdesign population

*Treatment Plant

capital cost more less

O/M cost more less

*H2S Corrosion and Odor Potential less more

Economics tend to favor multiple service per PU if they are within reasonable proximity. The

cost-effective separation distance is a function of local construction costs and system design.

However, the problems resulting from one homeowner receiving credits for power usage and

inherent tendencies of people to blame others for malfunction of the PU or service line

components should be expected. These types of problems can be overcome through

1


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management, arrangements which utilize direct power transmission through a separate power

meter and inclusion of service calls within the user charges. Such systems usually result in the

placement of the PU where there is a high degree of accessibility for service labor, but possibly

at a cost of excessive lengths of piping. With small lots or building sites and favorable terrainthis latter problem may be minimized.

Serviceability of the on-lot components is important to both minimize the time lost due to a

malfunction and keep the cost of inspection and maintenance to a minimum. Quick-disconnect

features are recommended both for the piping and the electrical connections, so that the service

person can quickly remove the unit for inspection and repair or replacement. With very shallow,

less than 1 m (3.3 ft), wetwells a simple union arrangement is often acceptable. With deeper

wetwells, slide-away coupling arrangements with slide-rail and lifting chains are more common.

With GP units complete manufacturer packages are generally employed which incorporate

simplified GP unit removal arrangements.

In residential developments safety problems are generally related to protection of the

homeowner and their neighbors. One of the most frequent concerns relates to the PU wetwell

cover. In the interest of providing a safe PU the wetwell covers shall incorporate locking

mechanisms which provide relief under emergency conditions. By proper venting of STEP units

through the septic tank and house roof vents accumulation of hazardous and potentially odorous

gases can be minimized.

Materials of construction must be capable of withstanding the environmental conditions of

service. GP systems are generally packaged in such a manner that these considerations have

been incorporated at the factory. STEP systems which are often designed and assembled locally

require a cognizance of the highly corrosive nature of septic tank effluent. All components of the

STEP system exposed to the atmosphere (not always submerged) must be highly resistant to

corrosion. Materials which have been acceptable for different components are listed below:

Septic tank and wetwell - concrete, plastic, coated steel

Valves - bronze, plastic


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Ancillary items - plastic, 316 stainless steel

Pump housing - cast iron, plastic, bronze, coated cast iron

Pump impellers - plastic, bronze, cast iron

Tank and wetwell cover - concrete, plastic, coated steel

Electrical connections to the main panel must be in accordance with local construction codes.

Approved underground wiring is recommended for both pump and control circuits and should be

provided with separate fuses or circuit breakers. The controls shall be located outside the house

in full view of the PU and contained in a lockable or tamper free and weatherproof circuit

breaker box. For single service units, PU power sources should not be metered separately since

minimum local billing charges will greatly exceed actual usage. The pump panel should have a

smaller fuse or breaker than the service panel Finally, the pump motor connections must be

water-tight.

Due to potential power outages in rural areas both STEP and GP installations should have

reserve holding- capacity. Single service GP installations generally provide a reserve storage

capacity of about 0.19 m3(50 gallons). Septic tanks usually have about 0.38 to 0.76 m3(100 to

200 gallons) or residual capacity due to the freeboard inherent to the construction. Additional

storage capacity may be required based on local conditions. 7ne loss of power in rural areas that

are served by individual wells and cisterns essentially eliminates the possibility for wastewater

generation because water supplies become unavailable. The minimum storage capacity required

is .19 m3(50 gal) unless local authorities require additional storage based on local conditions.

On-lot facility considerations should include the use of hydraulically similar PU equipment in

order to simplify design and O/M tasks. Spare parts and equipment inventories shall be

maintained as a minimum:

PUs Installed Spares Required

1-10 1

10-20 2

20-40 340-60 4

60-100 5

100-200 6

200 3%


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In addition, a complete supply of spare units of all system components must be maintained in

similar quantities to the above scale for complete PUs.

Part 4. Design Flows

Systems must be designed on the basis of the type of PU employed and peak flows from the

number of people to be served by the system. Figure I-3 indicates the recommended design flow

for the anticipated number of service connections. For the more predictable progressing-cavity

units, the design curve is based on the probability of simultaneous operations determined from

the operating experience of previous PU system developments. If a progressing-cavity unit is to

be installed and exhibits dynamic head-discharge (H-Q) significantly different from 0.7 l/s (11

gal/min) at high head, the curve should be adjusted accordingly. For centrifugal units in systems

of less than 30 total separate services the pump and system characteristics are the primary

determinants of the design flows to be used. In the range of 1 to 30 units the design flow should

always be more than a single pump operating against the minimum system head possible and no

more than 1.9 1/s (30 gal/min). The design must utilize the facility planning data on this subject

to determine water use or average persons per dwelling. If either information source or other

mitigating information, e.g., excessive lawn watering due to climatic conditions, indicates that

flows differ significantly from the average use, the engineer should adjust the design flows from

those listed below, and shown in Figure I-3 (centrifugal), accordingly.

No. Dwelling Units Design (Peak) Flow in m3/s x 10-3 (gal/min)

1 .9 (15)

10 1.9 (30)

50 2.7 (43)

100 4.7 (75)

200 8.2 (130)

300 11.4 (180)

A pressure sewer is normally designed to flow full at all times. In smaller installations there

may be relatively long periods of time where no flow win occur. During these periods an

opportunity exists for deposition of grease or solids and gas accumulation. The results of these

no-flow periods can pose serious problems if subsequent hydraulic conditions are unable to scour

the depositions and transport those materials and gas accumulations out of the system.


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FIGURE I-3. Recommended Design Flow


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GP system designers have employed peak design velocities of 0.6 m/s to 1.6 m/s (2 to 5 ft/s).

The minimum required peak design velocity for GP systems shall be 0.8 m/s (2.5 ft/s). For septic

tank effluents with greatly reduced solids and grease concentrations no peak velocity

requirements have been determined, but shall be at least 0.3 m/s (1 ft/s) to insure the scouring ofany suspended material. Use of other design velocities for either type of system is subject to the

approval of the Department of Environmental Regulation.

Part 5. Hydraulics

Plastic pipe has been shown to exhibit a Hazen-Williams roughness coefficient C in English

units of 155 to 160 with clean water. However, due to the nature of wastewater and the potential

for grease deposition and microbiological growth on the walls of pressure sewers, a reduced

value of 130 to 150 is recommended. By multiplying the Hazen-Williams C by 1.318 one can

obtain the Chezy C in English units.

Although polyvinyl chloride (PVC) pipe has been most widely used for pressure sewers, high

density polyethylene pipe (PE) has recently been employed in some installations. Roughness

coefficients for straight sections of both pipes are essentially identical. Although some use of

polybutylene for service lines has been reported, there is no present basis for its evaluation as a

mainline system.

PVC pipe with a pressure rating of 1,100 kPa (160 psi) will usually suffice for normal

pressure sewer systems utilizing PU equipment with centrifugal or progressing-cavity pumps

having a maximum dynamic head of less than 1,100 kPa (160 psi). However, due to potential

imperfections in manufacture and installation of pressure pipeline components, the ratio of

pressure pipe rating to the maximum pressure developed by the PU should not be less than 2:1.

The standard pressure sewer PVC pipes and their characteristics are shown in Table I-5. Both

rubber ring and solvent weld joints can be used if properly jointed per ASTM requirements.

High density polyethylene pipe (HDPE) has been used in. lieu of PVC in at least three

locations. This material has certain advantages and disadvantages when compared to PVC.

Longer pipe length with fewer joints are available but special joining techniques (butt-fusion) are

required. HDPE is similar to PVC in working pressure and roughness coefficient.


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TABLE I-5

PVC PIPE CHARACTERISTICS

SDR

26

SDR

21

SCHEDULE

40

SCHEDULE

80

SDR

(O.D./wall thickness) 26 21 VARIES WITH SIZE

WORKING PRESSURE 1,100 kPa(160 psi) 1,400 kPa(200 psi) VARIES WITHSIZE

NORMALLY USED

JOINTS RUBBER RING SOLVENT WELD

STANDARD LENGTH 6.1 meters (20 feet)

THERMAL

EXPANSION0.08 mm/m/C

(0.33 in./100ft/F)

PVC PIPE DESIGNATION

DATA


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The hydraulic design of a pressure sewer must take into account several factors. The most

noteworthy being the head-discharge characteristics of the PU. The simplest case is that of a

centrifugal STEP system. Pipe sizes should be selected which display the best combination of

low frictional headloss and reasonable velocity at the design flow. Most pressure sewer systemswill employ pipe sizes of increasing diameter when progressing from the origin toward the

terminus of the system. It is recommended that a centrifugal pump should not be specified under

conditions requiring greater than 85% of the available head when operating alone.

The following procedure is typically used to approximate the initial hydraulic design:

1. Determine the ultimate number of facilities to be served by the system.

2.

Choose a design peak flow value using Figure I-3.

3. Prepare a condensed plan and profile of proposed system.

4.

Evaluate the need for air release and pressure sustaining valves.

5. Plot hydraulic grade lines (HGL) corresponding to various pipe sizes. Any pipe size

which indicates an excessive total dynamic head (TDH) is sequentially discarded until a

proper one is found based on economics pressure limitations, and reasonable

approximation of pump characteristics. Pressure sustaining valves maintain positive

pressure, increase the TDH against which the pumps operate and prevent drainage of the

line (see Figure I-4).6. Prepare dynamic hydraulic grade line (HGL) based on previous determinations.

Individual pump units can then be selected based on site-specific head conditions and

desired flow rate. Individual pump characteristics can be tested for sufficiency by

checking the elevation difference between pump and dynamic HGL where the pump

lateral intersects the mainline.

Test:

a. Plot system-head curve of pump (including losses in service lines and fittings).

b.

Locate head requirements at design flow and determine adequacy of pump and suitable

pipe size.


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FIGURE I- 4

PIPE SIZING PROCEDURE


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The PU selection will depend upon the hydraulic profile of the system and the characteristic

pump curves chosen for the system. Thus, an analysis of the manifolded pump and pipe

networks should be determined for the proposed system. An analysis of the time dependent

alternations in the manifold systems characteristics as pumps turn on and off should be includedto determine the proposed system capabilities. Water hammer and surge analyses may be

necessary on large systems with higher pressures but are not normally a concern. Factors to be

taken into consideration in performing the analysis include:

operating capacity of pump chamber or wetwell

pump characteristics

distribution piping, materials and appurtenances.

Pressure sewer equipment manufacturers frequently have computer simulations available to

simplify the system analysis.

Part 6. Contingency Planning

As previously discussed in Chapter 1, Section A, Part 3 the contingency needs of GP units

are greater than for STEP units. Greater on-site storage capacity lessens O/M personnel

requirements by permitting repairs to be made during normal working hours and minimizing theneed for extra working shifts and the associated additional manpower. Connection to abandoned

soil-absorption systems where groundwater conditions are favorable, enlarged pump chambers or

wetwells with quick-disconnect arrangements, and adjoining overflow tanks with gravity

drainage back to the pumping chamber during normal operation are possible contingency

solutions which are simple and, therefore, practical. The requirements for an average days flow

storage is subject to local conditions. Most analyses of these requirements based on nationwide

electrical outage data, bare little relation to local conditions of electrical outages and anticipated

or experienced repair times for pressure sewer mains.

The problems of pressure sewer main breakage must be anticipated. Location of pressure

sewer mains in areas where damage is less likely, provision of detailed and accurate as-built

contractors plans, warning signs along route with offset markings, inductive wire burial with

pipe, and a stringent permit requirement for excavation work in proximity to pressure sewers

have been shown to be effective in eliminating pressure sewer main breakage. Management


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arrangements shall incorporate regulations which clarify the financial and repair responsibilities

for pressure sewer damages.

Contingency plans are subject to the review and approval of the Department ofEnvironmental Regulation.

Part 7. Mainline Appurtenances

The need for terminal and in-line cleanouts is a function of the design of the system. For

example, a pure dendriform design would require only one terminal cleanout arrangement, while

a multiple-cluster feeder design would require a terminal cleanout for each cluster. Cleanouts

and/or shutoff valves should be provided at all pipe junctions and at locations where pipe sizes

change. Subject to the approval of the Department, this requirement may be fulfilled in phases

for new developments. Consideration should also be given to angle points in the pressure sewer

and major pressure sewer main junctions. Beyond these specialized considerations the needs for

cleanouts and/or shutoff valves may be related to the available cleaning methods, contingencies

required for the system and the projected use or growth rate of the service population.

The previous discussion of in-line cleanouts is pertinent to shut-off valves and bypassing

arrangements. Pressure sewer main segment isolation for repair is necessary and the longerdistance between valve stations makes isolation more difficult. However, the use of an arbitrary

rule of maximum separation distance is often unnecessarily restrictive, e.g., a 120 to 150 m (400

to 500 ft.) requirement in a relatively rural area may service 4 or 5 connections, while in a more

dense development it may service 15 to 20 connections.

Therefore, in the absence of special needs for mechanical cleaning, pipe size changes, abrupt

changes in direction, or major main confluences, the spacing of inline shut-off valves need not be

less than every 183 m (600 ft) in high density areas and not more than 307 m (1000 ft) in low-

density areas. By utilizing simple meter box designs such as those shown in Chapter III with a

cleanout and valves, these mainline arrangements can be economical and simple to operate.


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Gas accumulations in pressure mains can increase the dynamic head resisting the PU. As

noted in Chapter I, Section A, Part 3 above the design should provide a continuous upward slope

on the pressure sewer main to maintain a positive pressure at all times, to avoid siphoning, air

accumulation and solids accumulation. In some areas, high points in the system cannotpractically be eliminated, and air release valves must be employed at the more pronounced

locations. With higher flow rates, minimum downstream slopes and short travel distances to

subsequent low points, the need for air release valves is marginal. The need for air release valves

should be closely examined for any downslopes in excess of ten percent (10%). Locations with

lesser slopes, where long downstream pipe volume is in excess of that which would be expected

to be pumped during one continuous pumping interval, may also require air release valves.

Adequate preventive measures should be taken to avoid the accumulation of gases and air in

pressure sewer mains. These include:

1. Sufficient purging after pressure sewer main filling and testing.

2. Submersion of PU pump intake to prevent siphoning or vortexing after shut-off.

3. Proper design to prevent undue retention time of wastes in pressure sewer where

biological and chemical activity may produce gases.

In areas where topographical considerations preclude elimination of high and low points in

the vertical alignment, pressure-sustaining or pressure-control valves are required. Constantpressure valves impose a constant control point to maintain all or part of the system under

pressure during no flow periods, while flow-responsive valves accomplish this same task and

also provide a reduced control pressure during active pumping periods. With relatively low head

PUs the flow-responsive type valve is more commonly employed.

Part 8: Treatment And Characteristics Of Low Pressure Sewer System Wastewaters

Effluent wastewater characteristics of GP and STEP systems are dependent upon the initial

wastewater characteristics entering the system from the service user. In consideration of the

pressure sewer systems presently in operation, both GP and STEP effluents have demonstrated a

high degree of treatability. Available data suggests that GP effluent wastewater characteristics

are of greater concentrations than commonly found in domestic wastewater. This is entirely due


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to absence of infiltration or inflow to the pressure sewer system.

Wastewater treatment facilities must be provided which are designed for the specific

wastewater expected from the pressure sewer if it discharges into a treatment facility exclusivelyfor these wastes. Consideration of the unique characteristics of the GP and STEP effluents

becomes less critical if these effluents are combined with gravity sewer wastewaters and do not

constitute a significant proportion of the total wastewater received for treatment.

Generally, treatment facilities which are constructed to treat GP or STEP wastewaters only

should be designed to anticipate influent wastewater characteristics as follows:

Treatment Facility Influent Characteristics

Parameter GP Systems STEP Systems

Average Range Average Range

BOD5mg/l 350 300-400 143 110-170

TSS, mg/l 350 300-400 75 50-100

FLOWS, gpcd 70 70

The only special concern during the treatment processes has been the need to minimize

liberation of hydrogen sulfide, H2S, if present by excess turbulence at the inlet to the treatment

plant. With conventional mechanical treatment facilities, the elimination of grit chambers,

comminutors and primary treatment processes may be offset by the need for preaeration or

chemical oxidation of H2S for STEP system wastewaters.

When a STEP system is designed to discharge into a conventional gravity sewer system, the

liberation of H2S at the junction structure and corrosion of unprotected concrete sewer pipe

immediately downstream of the junction must be considered. Consideration to H2S liberation

may also need to be given at GP discharges. The adverse effects should not be a great concern

unless the dissolved sulfide content of the STEP or GP wastewater attains a level of 0.1 mg/l or

greater concentrations at the outlet. In situations where the dissolved sulfide content of the STEP


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or GP wastewater exceeds 0.1 mg/I, a sulfide control system must be incorporated into the

pressure sewer system. Approximations of the dissolved sulfide content should be determined by

the methods published in the U.S. EPA Technology Transfer Process Design Manual for SulfideControl in Sanitary Sewerage Systems.

Standard pretreatment methods can be utilized to prevent corrosion and control odors in both

the collection system and the treatment plant. Several measures of pretreatment are presented in

the cited references. The design of the wastewater treatment facility being utilized should follow

standard procedures as outlined in Manual of Practice of the Water Pollution Control Federation

Wastewater Treatment Plant Design, U.S. EPA Technology Transfer Design Seminar Manual

Alternatives for Small Wastewater Treatment Systems as well as the U.S. EPA Sulfide

Control Manual and any other treatment plant design guidelines recommended by the State of

Florida Department of Environmental Regulation.

Part 9. Management Implications

Several management arrangements have been employed with pressure sewer systems. In

order to minimize the responsibility of the service users the Department of Environmental

Regulation requires that the operation and maintenance of the pressure sewer system be theresponsibility of a central management entity, be it public or private, having indicated prior

acceptance. Outside of discovery and reporting of system malfunctions, homeowners cannot

generally be relied upon to take a responsible role in management. Ordinances prohibiting

disposal of particularly troublesome articles, such as plastics, to the system are not universally

effective without strict enforcement by a strong central management entity.

The overall staffing of the management entity is a function of system size and the type of

entity. The actual field crews required for on-lot inspection and emergency repairs, pressure

sewer main inspection and preventive maintenance are usually comprised of two people with a

fully equipped truck. Some STEP systems have been operated and maintained by a one-person

crew, but normally two would be more desirable, especially for emergency repairs. These crews

shall be fully trained as to the equipment characteristics and functions by the manufacturers


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involved and supplied with O/M manuals. For systems with less than 100 services contractual

arrangements for O/M may be more economical because of insufficient demand to justify a

trained full-time operator.

Some suggested management characteristics already discussed within this chapter are:

1.

A single telephone number, for service calls.

2. Pumpout and disposal of septic tank residuals for STEP systems and GP wetwell

accumulations.

3. Periodic inspection of PU and septic tank residual accumulation.

4. Emergency repairs facilities for system malfunctions.

5. Pressure sewer valve inspection, testing and periodic cleaning.

6.

Maintenance of a sufficient spare part inventory.

In addition to specific training the persons responsible for the overall maintenance and

operation of a pressure sewer system should have some knowledge of:

1. Pump mechanics and operation.

2. Pipe handling and repair.

3.

Mechanics of fittings, valves, etc. and other components that comprise the on-site unitand system as a whole.

4. Customer relations.

5.

General operation of the pressure sewer system.

6. Installation of the system including on-lot facilities.

Routine annual inspections of on-lot facilities include removal and/or visual inspection of the

PU, controls, warning system and other ancillary items, including the electrical connections. For

STEP systems a visual check of sludge and scum accumulations in the septic tank should be

made at the same time. Routine inspection of pressure sewer main appurtenances should be

made a requirement. Shut-off, air-release, and pressure-sustaining valves should be inspected at

least once per month and exercised. Maintenance of air release valve assemblies should be

performed as dictated by these inspections. Pressure sewer main flushing should be performed

as required and with the necessary precautions for preventing cross-connections.


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Pressure sewer systems shall be administrated in the same manner as gravity sewers or

treatment facilities. A central authority shall maintain ownership and responsibility for all

components of the pressure sewer system.

The same central authority shall be responsible for collection, treatment and disposal of

septage and other residual solids in accordance with all applicable state and local agency rules

and regulations.

Section B. BASIC DESIGN

Part 1. Summary

There are basic procedures for the design of pressure sewer systems which are common to all

situations. The example provided in Part 2 is presented to indicate a basic design sequence for

existing and new developments.

Part 2. Design Sequence

The design sequence may typically be as follows:

a. Determine required data where possible for the planning area including the location of

dwellings, population (present and design), water use, soils profiles, groundwater and

surface water characteristics, present wastewater disposal facilities and problem

locations, climate, and topography.

b. Determine State and local regulations and available management entities.

c. Determine location and condition of existing septic tank systems, where applicable.

d. Evaluate alternative treatment plant designs and locations and choose the most cost-

effective.

e.

Prepare a preliminary layout of pressure sewer mains based on minimized pipe lengths to

sewer design population, the cost-effectiveness of serving fringe units (where applicable)

which require long piping reaches vs. continued or modified on-site system service,

potential for phasing construction of feeder mains and the potential for multiple service

PUs.


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f.

Locate and determine minimum quantity of air-release and pressure-sustaining valves,

in-line and terminal cleanouts and mainline shut-off valves.

g. Analyze alternative on-lot systems with respect to PU, control and alarm equipment,

contingency systems, residuals disposal plan, and capital and operating costs. Determinemost cost-effective generic type system and potential for phasing.

h. Where available determine design flows based on present local data, theoretical flow

patterns and type of equipment chosen.

i. Perform hydraulic analysis to finally determine pipe sizes, transition points, valve and

cleanout locations and anticipated needs.

j. Analyze alternative management systems.

k. Review plan with Department of Environmental Regulation.


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CHAPTER II

ON-LOT FACILITY CONSTRUCTION

Section A. SEPTIC TANK AND WETWELL

Part 1. General

As discussed in Chapter I, Section A, Part 3, both grinder pump (GP) and septic tank effluent

pump (STEP) systems should have reserve holding capacities. Individual resident GP

installations generally provide a reserve storage capacity of about 0.19m3 (50 gallons) while

septic tanks generally have about 0.38 to 0.76 m3(100 to 200 gallons) of residual capacity due to

the freeboard inherent in the construction. The pressuration unit (PU) reserve capacity is shown

in Figure II-1 as the volume available for storage between the elevations of the high water alarm

float switch and the invert of the overflow pipe. Figure II-2 indicates the freeboard within the

septic tank generally available for reserve storage for a typical STEP system with the PU located

either within or adjoining the septic tank.

Part 2. Sizing

Wetwell sizing is normally a function of required reserve capacity and PU hydrauliccharacteristics. Installations which serve more than two residences per PU often require smaller

amounts of reserve capacity per residence than would PUs which serve individual residents.

Large installations may consider employment of standby power generation facilities rather than

provide large reserve capacity.

Part 3. Septic Tank Structural Design

Owing to the presence of a high water table within many areas of the State of Florida, the

structural design of septic tanks should include hydrostatic loading in addition to the soil loading

upon the septic tank walls, floor and roof. Under most circumstances, septic tanks are located in

areas not subject to vehicular traffic, however, occasionally it may be necessary for a vehicle to

pass over an existing septic tank and, therefore, the septic tank roof should be of strength to resist

collapse. Septic tanks shall be provided which have an approved structural design.


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FIGURE II-1

TYPICAL PRESSURIZATION UNIT (PU)

INSTALLATION


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FIGURE II-2

TYPICAL SEPTIC TANK EFFLUENT PUMPSYSTEMS


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Part 4. Corrosion of Materials Used in Septic Tank and Wetwell Construction

Septic tank and wetwell interior wall surfaces, whether partly submerged or covered with

condensation, are subject to corrosion from several sources. Corrosive agents may be present in

the water supply itself, such as chlorides, as well as the polluting material within the wastewater.As sewage is detained in the septic tank for long periods of time, oxygen is depleted from the

wastewater and anaerobic conditions develop. Hydrogen sulfide, H2S, reacts biologically with

bacterial organisms on moist interior surfaces to form sulfuric acid, H2SO4. Materials used in

septic tank construction should be shown suitable by test, experience, or analysis acceptable to

the reviewing agency.

Part 5. Testing

To insure water tightness, septic tanks shall be tested by filling with water to the soffit, left

standing for twenty-four hours and examined for leakage. This is most important when installed

in an area of high groundwater. Some types of tanks will require only testing of a representative

sample, while with other types, each tank should be tested. Concrete and fiberglass septic tanks

are normally of the second category.

Part 6. Installation of Septic Tanks

Septic tanks shall be installed in accordance with the sound engineering practice. Theexcavation backfill adjacent to the installed septic tank should be placed in 150 mm (6 inch) lifts

watered to optimum and compacted to 90% of relative density. Stones or debris having a

diameter of 102 mm (four inches) or larger should not be included in the backfill material.

Backfill in the vicinity of the septic tank inlet and outlet piping should be manually placed and

consist of crushed rock to a depth of 150 mm (6 inches) over the inlet or outlet pipes with the

remaining backfill placed in the same manner as adjacent to the septic tank. Septic tanks

installed in soft or yielding soils should be bedded on crushed rock having a thickness of not less

than 150 mm (6 inches). When septic tanks are installed in areas where groundwater will be

above the septic tank floor the septic tank shall be secured against floatation.


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Section B. SEPTIC TANK CONSTRUCION

Part 1. Concrete Septic Tanks

Concrete septic tanks shall be constructed in accordance with recommendations of theAmerican Concrete Institute (ACI) or an approved equal. A study by the U.S. Public Health

Service (1) was made on concrete septic tanks ranging in age of field use from one-half to 39

years. Of the 150 tanks inspected, 91% were judged to be in good or excellent condition with

respect to the concrete with some showing corrosion at and above the water line. Various

coatings have been applied to the interior of the septic tank above the operating water level but

have shown little success in reducing corrosion.

Part 2. Plastic Septic Tanks

Septic tanks are available in fiberglass, polyethylene and Acrylonitrile-butadiene-styrene

(ABS) construction materials with fiberglass reinforced plastic being the most common.

Fiberglass septic tanks shall be constructed according to ASTM D3299 or International

Association of Plumbing and Mechanical Official (IAPMO) IGC3-74 as applicable. Wall and

bottom thicknesses will be determined by the specific application to meet the worst structural

loading condition. Because of their light weight, plastic septic tank installations should consider

antiflotation measures.

Deterioration of fiberglass has been known to occur by wicking along the glass fibers shouldfiberglass become exposed to moisture. Wicking may be reduced by application of resin rich

coating or a gel coat applied to all surfaces.

Part 3. Metal Septic Tanks

Common carbon steel with a coal tar epoxy coating has been used for GP wetwells and septic

tanks. Prior to fabrication, the steel should be sand- or shotblasted to a white metal finish as

recommended by the steel structurals painting specification SP-5-63 or NACE #2. After

cleaning, fabrication, inspection and spot recleaning, the surface must be coated before oxidation

can reoccur. Coal tar epoxy or bituminous products are often specified and applied in one or two

coats to a dry film thickness of 0.2 mm (8 mils.). Magnesium anodes are normally used in

conjunction with steel tanks for cathodic protection.


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Part 4. Existing Septic Tanks

On STEP systems, some existing septic tanks may be used. A careful inspection of the septic

tank is required. As septic tanks often leak infiltration can occur if installed in an area of high

ground water. The tanks should be emptied, the inlet and outlet devices inspected, and effects ofcorrosion examined. While emptied, smoke testing will help determine if structural cracks exist.

If the existing septic tank has failed to remain watertight it should be rehabilitated or replaced.

Part 5. Inlets and Outlets

Grinder pump and STEP wetwell inlets have been constructed either as a straight pipe or tee

entering the tank. Experience has not shown either design to be preferable. Required ventilation

of the GP or STEP wetwell internal atmosphere is usually through the roof vent of the service

connection. STEP wetwells may be designed as an integral part of the septic tank structure as

shown in Figure II-2.

Part 6. Septic Tank Risers and Wetwell Covers

Septic tank risers and wetwell covers shall be secured to preclude desired removal, but be

provided sufficient clearance to vent hydrostatic pressure should a check valve fail and backflow

enter the tank, unless other forms of pressure relief are provided. Unauthorized removal of the

septic tank riser or wetwell covers should be discouraged through use of a tamper-resistant

construction or locking device.

Section C. APPURTENANCES

Part 1. Grinder Pumps

Submersible centrifugal or semi-positive displacement (SPD) progressing cavity screw-type

pumps having ratings within the range of 745 to 1,490 watts (1 to 2 horsepower) are normally

specified. The performance for the two types of pumps are different in respect to capacities and

shut-off head. The submersible centrifugal pump has generally a higher flow producing capacity

at low heads while the SPD pump has the ability to generate higher pressures and more

predictable flows at higher heads as shown in Figure II-4. For clustered service connections

submersible centrifugal grinder pumps are available with rating between 2,240 and 3,730 watts

(3 and 5 horsepower). The SPD pump is not presently available with ratings exceeding 750 watts

(1 horsepower).


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FIGURE II-4

TYPICAL HEAD-FLOW CHARACTERISTICS FOR

CENTRIFUGAL AND SIMI-POSITIVE DISPLACEMENT PUMPS


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Grinder pump units must be capable of comminuting all material normally found in domestic

or commercial wastewater, including reasonable amounts of foreign objects such as glass,

eggshells, sanitary napkins and disposable diapers into particles that will pass through the 32mm(1-1/4-inch) standard discharge piping and downstream valves. Stationary and rotating cutter

blades on bases should be made of hardened stainless steel.

Single-phase motors are available in 208 or 230 volts and shall be of the capacitor

start/capacitor run type for high starting torque. Three-phase motors are available in 208, 230,

460 or 575 volts. A.U GPs shall be standard commercial shop-tested to include visual

inspection to confirm construction in accordance with the specifications for correct model,

horsepower, cord length, impeller size, voltage, phase and hertz. The pump and seal housing

chambers should be tested for moisture and insulation defects. After connection of the discharge

piping, the GP should be submerged and amperage readings taken in each electrical lead to check

for an imbalanced stator winding.

Part 2. Effluent Pumps

Effluent pumps shall be of cast iron, bronze, and/or plastic construction of the centrifugal

type with submersible motor. The pump shall be mounted in the pump wetwell or septic tank on

three integral support feet or base. Effluent pumps ratings range from 185 to 1,490 watts (1/4 to2 horsepower), depending upon the dynamic head and flow capacity requirements. Effluent

pumps with ratings up to 560 watts (3/4 horsepower) can operate on 115 or 230 volt sources

while effluent pumps with ratings over 560 watts (3/4 horsepower) require 230 volt service.

Effluent pumps are capacitor start with either permanent split capacitor or split phase motors.

Effluent pump motor starters and capacitors can be located in the motor or adjacent housing.

Either a control box housing or a junction box is required to connect the pump and level controls

to the service users power source.

Effluent pumps shall undergo the same testing required for grinder pumps as listed in

Chapter H, Section C, Part 1.


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Part 3. Wetwell Appurtenances

a) Internal discharge piping

Grinder pump systems may utilize galvanized iron pipe or schedule 80 PVC pipe for internal

discharge piping. Due to the severe corrosion potential of septic tank effluent internal dischargepiping for STEP system should be schedule 80 PVC or equal. The standard size of internal

piping is normally 32 to 38 mm. (1-1/4 inch to 1-1/2 inch) diameter for 1,490 watts (2

horsepower) or less rated pumps. For 2,240 to 3,730 watts (3 to 5 horsepower) rated pumps 51

to 64mm (2 inch to 2 1/2 inch) diameter internal discharge piping is normally required.

b) Check valves

Check valves used in both grinder and effluent systems are ball or flapper type with valve

bodies constructed of plastic or bronze. Balls and flappers are available in rubber, plastic or

metal. Due to possible physical damage to the threaded connections of plastic check valves

moderate care must be taken.

c) Hose connections

Hose connection may be used in GP or STEP systems as part of the internal discharge piping.

Flexible hose connection must be secured to the discharge pipe nipple or hose to iron pipe

adapter and sealed with a type 316 stainless steel clamp. Couplings may also be threaded to the

pump discharge and connected, to the flexible hose.

d) Gate or ball valves

A gate or ball valve will normally be installed inside the pump chamber or may be located

outside the pump chamber if required by local codes. Gate or ball valves constructed of bronze

or plastic are preferred. If the valve is located more than one foot from the top of the pump

chamber, an approved riser should be furnished to open and close the valve.

e) Quick disconnect couplings

Rail type mountings of effluent and grinder pumps should be installed with a quick

disconnect coupling. This type of coupling is used when the discharge pipe is located 0.9 meter

(3 feet) or deeper in the pump chamber. Discharge couplings are made of cast iron with rubber

0-rings or diaphragm sealing flanges.


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f) Level sensors

There are four basic types of level sensors used with GP and STEP systems. They are:

1. Mercury level control - Mercury level control switches contain a mercury contact

switch encased within a polyurethane ball In the simplex system three separate

switches are required with each switch designated to either turn the pump off, on, or

activate a high water alarm. Recently, a differential mercury switch has been

introduced which has combined the on and off function within the mercury control.

A second mercury switch is still required to activate the high water alarm.

2. Magnetic-weight displacement - Magnetic weight displacement switches have been

used in both GP and STEP systems. As the water level rises in the wetwell the

magnetic weights are moved upward to allow a magnetic contact and start the pump.

As the water level in the wetwell recedes, the weight of the plastic weights

disengages the switch, turning the pump off. A mercury level control switch is used

in conjunction with a weight displacement type for the high water alarm.

3. Pressure sensing switches - Pressure sensing switches have been used in GP systems.

This type of switch is operated by hydrostatic pressure as the water level rises and

recedes within the wetwell. A similar switch is installed as a high water alarm.Pressure sensing switches must be vented to the atmosphere.

4.

Diaphragm switch - Diaphragm switches are used primarily with sump pumps and

sewage ejectors but can be used with effluent pumps. Diaphragm switches must be

vented to the atmosphere. A second diaphragm switch, mercury level control switch

or pressure sensing switch would be required to activate the high water alarm. The

diaphragm switch is not recommended for GP systems due to the potential of solids

build-up around the diaphragm.


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g. Sealing of adaptors passing through chamber

Steel couplings should be butt welded to the sidewall of steel wetwell to provide outlets for

the discharge piping and power conduits. For fiberglass wetwells the outlet coupling should be

either fiberglass bonded and coated or bolted to the interior wall with type 316 stainless steelbolts. Fittings should then be covered with an approved silicone sealant.

Section D. ELECTRICAL

Part 1. Grinder Pump Control System

Since the single phase submersible centrifugal grinder pump has a capacitor start type motor,

the capacitors and start relays must be located in a separate control panel enclosure. This control

panel can be located either outside (NEMA 3 enclosure) or inside (NEMA 1 enclosure) the

service location. In the interest of safety it is recommended that the control panel enclosure be

placed within sight of the pump wetwell. The control panel should include, but not be limited to,

a magnetic starter with ambient compensated bimetallic overload relay. The relay should have a

test button for simulation of overload trip and manual reset button. Fault protection should be

provided via a molded case magnetic circuit breaker with internal common trip or multiple poles.

A hand-off-automatic toggle switch for hand operation with a green light to indicate the pump-

running mode should be provided for each GP and mounted on a bracket inside the control panel

enclosure. The control panel enclosure should be of high quality construction that meets Stateand local safety codes as well as national electrical codes. Should there be a power failure, GP

malfunction, or flooded wetwell, pump controls and wiring must be accessible and comply with

all code regulations to insure safety of the service user or operating personnel. As an alternate an

explosion-proof combination motor control/junction box may be installed inside the GP wetwell.

Semi-positive displacement pumps having the starter and capacitor located in the pump core

require only a standard junction box hook-up to the power source.

Most grinder pumps applications require either 208 or 230 volt single phase power source and

the designer must be assured that this power requirement is comparable with the service users

power distribution system. The recommendations under this sub-Section D, Part I are also

applicable to three phase installations.


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Part 2. Septic Tank Effluent Pump Control Systems

Effluent pump starters and capacitors are located inside the motor housing and do not require

a separate control panel containing these components. Depending upon the type of wastewaterlevel control sensors and other components utilized a separate control panel may or may not be

required.

Part 3. Pump and Alarm Systems Wiring

Wiring to connect GP or STEP systems to the power source should be suitable to direct

burial and comply with State and local electrical codes. Wiring for the level sensors and control

panel (if required) must also comply with these requirements.

It is recommended that an audio and/or visual high water alarm be utilized with both the GP

and STEP systems. The purpose of this alarm is to alert the service user of a system malfunction

and to call the service authority. The alum should be designed so that the service user can met

the audio alarm after a malfunction, but not disable it for future malfunctions. The alarm system

can be mounted outside or inside the service location. In some cases, one alarm will be installed

inside the service location with a backup alarm located outside the service location.

Section E. EXISTING SEPTIC TANK OVERFLOWS AND DRAINFIELD LINES

Part 1. Grinder Pumps

Connection of grinder pump installations to an overflow or drainfield system must be

approved by the Department of Environmental Regulation. If an overflow to an existing

drainfield is not feasible and is required by State or local codes the following methods are

recommended.

a) Holding tank

A holding tank constructed of coated steel, plastic or concrete may be installed adjacent

to the GP installation and connected as an overflow device. The addition of a holding tank

will reduce the cost-effectiveness of the entire system and will require the holding tank

contents to be removed when the tank has filled. The contents of the holding tank shall be

removed by pumping into a tank truck or returned into the inlet of the GP system.


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b) Existing on-site septic tank

If an existing on-site septic tank is available -d in a condition as described in Section B, Part

4 it may be emptied, inspected and rehabilitated as necessary for use as a holding tank. This isbased on the assumption that GP system service can be restored within a reasonable time period.

Emergency storage in the GP wetwell should be at least to 6 to 8 hours depending upon usage.

Part 2. STEP Systems

An advantage of the STEP System concept over the GP system is the additional storage

capacity available. In addition to the excess storage in the pump wetwell, there is also the excess

storage capacity of the septic tank. These combined capacities equate to about 24 hours of

available storage. Since most of the settleable and floatable solids have remained in the septic

tank, the clarified effluent can be disposed of if required by State or local codes in the following

manner.

a) Existing drainfield

If a previously existing drainfield is in reasonable condition, the overflow may be

connected to the drainfield for emergency usage. This can present a potential problem if t-he

seasonal water table or flooding conditions in the area were the cause of the original

drainfield failure. In these incidences, the ground or surface water could backflow into the

pump wetwell, unless a backflow valve were installed, requiring the pump to run forextended periods, decrease the life of the PU and generate excess flows at the wastewater

treatment facility.

b) New drainfield

If a previously existing drainfield is unacceptable or unavailable, a new drainage field

can be provided if required but it will be susceptible to the same conditions noted for existing

drainage fields.

Part 3. Venting

The standard roof venting system will normally be adequate for a STEP or GP system. It is

not feasible to include a vent pipe at the ST-EP wetwell due to potentially objectionable odors.

Vent piping may be extended to the old drainfield system as a back-up for either STEP or GP

systems.


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Section F. BUILDING SEWER

Piping from the wastewater source to the wetwell or septic tank shall be installed by a

licensed contractor. The installation is required to comply with State and local codes. Special

attention should be given to the inspection of the building sewer to ensure watertight joints and

grade that provides gravity flows.

Section G. SERVICE LINES

Part 1. General

The service line piping between the PU wetwell discharge coupling and the pressure sewer

will usually vary between 32 and 51mm (1-1/4 and 2-inch) in diameter. The 32 mm (1-1/4 inch)

pipe is the nominal diameter recognized to offer the best compromise among costs, necessary

scouring velocities and minimum head loss considerations for GP systems. If larger horsepower

pumps are used to attain higher flow capacities 38 to 51 mm (1-1/2 to 2 inches) may be

considered.

Minimum flow velocities for pressure sewer mains are discussed in Chapter 1, Section A,

Part 5.

The service lines should be rated to withstand short term operating pressures of 1,100 kPa

(160 psi) or twice the calculated operating pressure which ever is the greater. Potential long term

high pressures resulting from plugged force mains or closed valves must be identified and

remedied within a reasonable period of time. It is recommended that service lines be tested at themaximum PU shut-off head pressure prior to operation.

Part 2. Service Line Materials

PVC Schedule 40 or Schedule SDR-21 with solvent weld joints are normally used for service

lines in conjunction with Schedule 40 fittings. Some polyethylene (PE) pipe service lines have

been installed using mechanical fittings. Polyethylene pipe must be installed so as not to kink

the pipe and cause a restriction.

It is recommended that the location of the service line be identified to reduce potential

damage to the service line by mechanical excavation.

Part 3. Check Valves

An approved check valve should be installed in the internal piping of the PU on the discharge

side of either the GP or STEP system. However, a redundant check valve may be installed


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elsewhere between the discharge coupling of the wetwell and the pressure sewer main

connection. The check valve may be located on the service line either directly outside the pump

wetwell or near the pressure sewer main connection.It is recommended that check valves be used to prevent siphoning at the pump wetwell where

a minimum or negative hydrostatic head is encountered. A check valve will also prevent leakage

past the check valve in the event of a water hammer phenomena. This is particularly important if

the primary check valve is located in the horizontal position.

Part 4. On/Off Valves and Corporation Stops

A gate or ball valve will normally be located in the PU wetwell to prevent backflow when the

PU is removed for service. Additionally, a corporation stop or U valve is usually installed near

the service line/pressure sewer main connection to isolate the service line. The most common

type is a corporation stop.

Part 5. Service Line Installations

Service lines must be installed at a depth sufficient to prevent any mechanical damage but

not less than 305 mm (1 foot).

In most applications service lines will slope upward to the pressure sewer main connection.

In some cases where the service lines may slope downward a spring loaded check valve should

be installed in the PU wetwell to minimize potential siphoning problems.

Part 6. Separation of Waterlines and Street Crossings

Pressure sewer service lines and potable water supply piping shall be installed with at least

3m (10-foot) horizontal separations and/or pass State and local codes. Pressure sewer service

lines and potable supply lines shall be identified by silver markings or color code. Where

pressure sewer mains are installed on one side of the street, service line connections from the

opposite side of the street should be installed by boring, if the street has been surfaced, or

installed within a bored casing in heavily trafficked areas. The potable water supply line and

pressure sewer service line may be bored beneath the street surface in the same proximity

provided that either line is installed in an approved casing.


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Section H. CONNECTION TO PRESSURE SEWER MAIN

Part 1. General

The alternatives for installing connections from the service lines to the pressure sewer mainare to wet tap the service line as the service connections are required or to provide a plugged

connecting wye or tee on the pressure sewer main at the time of construction. If wyes or tees are

provided at the time of pressure sewer construction the location of the connection must be

identified to avoid excessive excavation to locate connection points for future use. Since the

majority of service line and pressure sewer mains are constructed using PVC or PE materials this

Section is restricted to a discussion of compatible materials. However, similar connections could

be made were other non-plastic materials and compatible fittings utilized.

Part 2. Connection Methods

a) WYE and TEE connections

Wye and tee saddles are available to install 32 to 51 mm (1-1/4 to 2-inch) I.D. service

lines to the pressure sewer main. The pressure sewer main in the street or right of way

location can vary between 38 and 305 mm (1-1/2-inch and 12-inch) I.D.

b) Wet tap connection

A popular method of connection of PVC service lines to a PVC pressure sewer main is

by wet tapping and installation of a tee connection. Solvent weld service connections of thistype are available in 13 to 51 mm (l/2 to 2- inch) diameters.

c) Polyethylene service lines

Polyethylene pipe cannot be solvent welded but must be heat fused to provide

installation of connecting service lines. Polyethylene can form a solid joint at high

temperatures so that the joint itself is stronger than the pipe wall. A variety of transition

fittings for polyethylene pipe is available.

Part 3. Valves

As previously stated in Chapter II, Section G, Part 4 a corporation stop or U valve should be

located at the street or property line to isolate the service line from the pressure sewer main. The

valve riser and cap should be located out of access of road traffic to prevent damage to the riser


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which could, in turn, crush the service line. Some pressure sewers do not provide a riser or valve

box to locate or service the check valve located near the street on the assumption that failure

would be a rare occurrence and that these components could, if necessary be located, excavated

and repaired.

Section I. PIPE INSTALLATION SERVICE

Service lines can be jointed on the surface and then placed into the excavated trench. Pipes

shall be jointed in accordance with the manufacturers printed instructions.

The trench should not be excavated for a distance greater than can be backfilled during the

same day of excavation.

It is not expected that the service line and valves will require any service under normal

operating- conditions. Occasionally, the service line may be broken due to a mechanical

excavation in the area or possibly an earth slide. If this happens, the service line can be isolated.


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determine the sustained pressure allowable for the anticipated wastewater temperature and

should be considered if the wastewater temperature will be significantly above the standard

rating temperature.

The sustained pressure capacity of PVC pressure pipe is also a function of the length -oftime the sustained pressure acts upon the pipe and must be considered in the design of the

pressure sewer main. Short-term pressure surges considerably higher than the long-term

pressure rating of the pipe are easily withstood without damage. For example, Class 150

PVC pressure pipe conforming to AWWA C900 will withstand an internal pressure of 5200

kPa (755 psi) for about one minute but will burst at the same pressure in about five minutes.

The same pipe will however normally carry an internal working pressure of 1034 kPa (150

psi) throughout the -design period without failure. The design of PVC pressure pipe must be

based on the long-term working pressure of the pipe for pressure sewer main installations.

PVC pressure pipe joints may be flexible using elastomeric seals or cemented. Joints should

conform to the requirements of ASTNI F477, ASTM D3139, ASTM F545, or ASTM D2564.

c) Polyethylene (PE) pressure pipe

In general PE pressure pipe performs in a manner very similar to PVC pressure pipe. PE

pressure pipe should be manufactured in accordance with the requirements of either ASTM

D2239, D3035 or AWWA C901. Unlike PVC pressure pipe PE pressure pipe joints cannot

be solvent welded but must be fusion-welded together in accordance with the requirements

of AST-M D3261.

d) Acrylonitrile-butadiene-styrene

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